Magnesium treated ferritic stainless steels



Patented Nov. 4, 1952 MAGNESIUM TREATED FERRITIC STAINLESS STEELS Nicholas A. Ziegler, James Goldsmith, and

Alvin F. Lahr,'Chicag0, Ill., ass'ignors to Crane Co., Chicago, 111., a corporation of Illinois No Drawing. Application october 25, 1950, Serial No. 192,141

This invention relates toa process in the treatment of steels and, more particularly, it is concerned with a magnesium treatment of steels of the ferritic stainless steel type.

At the outset, it is well known that ferritic stainless steels, of the type having 28 chromium, 3% nickel, and 1.5% molybdenum, have excellent corrosion resistance against many corrosive environments. However, their ductility (as measured by the elongation and reduction of area) is quite low. For this reason, the use of this alloy frequently is avoided, which is particularly unfortunate in those cases where from a corrosion standpoint it might be th best material to use. However, we have discovered that by treating this alloy with about 0.25% magnesium, its ductility is considerably improved, as shown by the following table:

pon blocks, from which the test bar blanks were cut off. The steel usually identified by those skilled in the art as a stainless steel of the type having to chromium, a trace to 4% nickel, a trace to 2% molybdenum, up to .2% carbon, with the usual amounts of silicon, manganese, sulphur and phosphorus, with the balance essentially iron was treated by adding to the metal in its molten condition from 0.1 to 0.4% molybdenum. It resulted in a desirable sound and gasfree metal. There was high ductility in th ascast condition, expressed by at least 10% elongation and at least 10% reduction of area. Molybdenum may be used alone with acceptable results, or it may b combined, if desired, with nitrogen with good results. Prior to machining the test bars, they were heat treated by air cooling from 1800 Fahrenheit. Heat Nos. 6271, 6272, and 6274 Table I Hardness T. S. Y. P. P. L. B. S E]. R. A. Serial Heat p. s. i. p. s. i p. s. i. p. s. 1 N Percent Percent It should be understood that the foregoing table is a summation of the physical propertiesof four heats of a nominal composition 28% chromium, 3% nickel, 1.5% molybdenum.

Each figure is an average of two tests.

Heat No. 6271 (a) was made from a commercial foundry scrap and killed with about 2 pounds per ton of aluminum.

Heat No. 6272 (b) was made from a commercial foundry scrap and killed with about 0.25% of magnesium, added as 80% nickel-20% magnesium master alloy.

Heat No. 6273(0) was made of 33% of commercial foundry scrap and balance-new materials, including 28 pounds of nitrogen-bearing (0.7% Na, Cr) ferro-chromium and was killed with about 2 pounds per ton of aluminum.

Heat No. 6274 (d) was made of 33% of commercial foundry scrap and balancenew materials, including 28 pounds of nitrogen-bearing (0.7% nitrogen, 70% chromium) mium, and was killed with about 0.25% magnesium, added as nickel-20% magnesium master alloy.

All four of these heats were prepared in pound heats and cast in conventional test couferro-chrowere sound, whereas heat No. 6273 was found to be porous or gassy, although portions could be found sufficiently sound for making reliable test bars. In these tests, measuring elongation and reduction of area by a static test a .505 inch diameter, 2-inch gauge tensile test bar was employed.

Referring again to the above table, it is apparent that the tensile strength, yield point, proportional limit, breaking strength, and hardness of the four heats (within the normal experimental error) are not too different. On th other hand, elongation and reduction of area of the two magnesium killed steels (Nos. 6272 and6274) are considerably higher (at least twice or more) than those of the two corresponding aluminum killed steels (Nos. 6271 and 6273). Moreover, gassiness of the nitrogen-bearing, aluminumkilled steel (No. 6273) was completely eliminated by magnesium treatment (in heat No. 6274).

Having thus described our process and the resultant article, we claim:

1. Article of manufacture made of a steel of a composition having 25 to 30% chromium, a trace to 4% nickel, a trace to 2% molybdenum, up to 0.2% carbon, the usual amounts of silicon,

manganese, sulphur, and phosphorus and the balance essentially iron treated in molten condition by an addition of 0.1 to 0.4% magnesium, said article being characterized by soundness and freedom from gas, as wel1 as by a high degree of ductility in the cast condition, expressed by at least 10% elongation and at least 10% reduction of area, measured by a static test of 0.505-inch diameter, 2-inch gauge tensile test bar.

2. Article of manufacture made of a steel of a composition having 25 to 30% chromium, a trace to 4% nickel, a trace to 2% molybdenum, up to 0.2% carbon, the usual amounts of silicon, manganese, sulphur and phosphorus, a trace to 0.2% of nitrogen, and balance essentially iron treated in molten condition by an addition of 0.1 to 0.4% magnesium, said article being characterized by soundness and freedom from gas, as well as by a high degree of ductility in the cast condition, expressed by at least 10% elongation and at least 10% reduction of area, measured by 4 a static test of a 0.505-inch diameter, 2-inch gauge tensile test bar.

NICHOLAS A. ZIEGLER. JAMES R. GOLDSMITH. ALVIN F. LAHR.

REFERENCES CITED The following references are of record in the file of this patent:

OTHER REFERENCES Alloys of Iron and Chromium, vol. II, High Chromium, page 223. Edited by Kinzel et al. Published in 1940 by the McGraw-Hill Book Co., New York. 

1. ARTICLE OF MANUFACTURE MADE OF STEEL OF A COMPOSITION HAVING 25 TO 30% CHROMIUM, A TRACT TO 4% NICKEL, A TRACE TO 2% MOLYBDENUM, UP TO 0.2% CARBON, THE USAL AMOUNTS OF SILICON, MANAGANES, SULPHUR, AND PHOSPHORUS AND THE BALANCE ESSENTIALLY IRON TREATED IN MOLTEN CONDITION BY ADDITION OF 0.1 TO 0.4% MAGNESIUM, SAID ARTICLE BEING CHARACTERIZED BY SONDNESS AND FREEDOM FROM GAS, AS WELL AS BY A HIGH DEGREE OF DUCTILITY IN THE CAST CONDITION, EXPRESSED BY AT LEAST 10%, ELOLNGATION AND AT LEAST 10% REDUCTION OF AREA, MEASURED BY A STATIC TEST OF 0.505-INCH DIAMETER, 2-INCH GAUGE TENSILE TEST BAR. 